Through the Swedish Pat. No. 350,919 (corresponding to U.S. Pat. No. 3,850,405) it is known to provide work tables for machine tools with T-grooved clamping bars which are vertically movable in grooves provided in the table, said clamping bars acting on one or two clamping bolts for clamping workpieces on the table. The clamping bars are operated by, for example, compressed-air cylinders. The clamping bars can assume inclined positions in their grooves in the table, i.e. be raised or lowered more at one end then at the other. In this way height differences between two clamping points along the bar are automatically compensated for, or differences in the effective length of the clamping bolts, which length is usually adjusted by means of nuts threaded onto the bolts and co-operating with clamping irons which clamp the workpiece. This gives a very quick and convenient clamping of workpieces
For work tables of this kind it is usual to provide, in its top surface serving as the work surface, a plurality of fixed, conventional T-grooves and only one movable, T-grooved clamping bar. This is necessitated both with a view to the costs involved, and the space required for the clamping bar and the associated compressed-air cylinders and power transmitting devices. A resulting limitation is, therefore, that an automatic height compensation can only be obtained at two points which must be situated along the single movable clamping bar. Further, the height required for this type of work table is considerable, which renders it unsuitable for certain types of machine tool.
A solution to the problem of obtaining both a low building height, and height compensation when clamping is done at more than two points, is suggested in the Swedish Pat. No. 7604795-0. In this case, movable clamping bars are used which have been made flexible by being composed of a number of short sections connected to each other by means of an elastic material, each section being individually acted on by power transmitting devices. However, this, too, represents an expensive design which is suitable chiefly for exacting clamping conditions and expensive machine tools such as, for example, milling machines.